The Oscillatory Motion of Jupiter's Polar Cyclones Results From Vorticity Dynamics

TL;DR

This paper investigates the oscillatory behavior of Jupiter's polar cyclones, revealing that vorticity-gradient forces from mutual interactions and planetary vorticity variations drive their long-term oscillations, supported by observational data and modeling.

Contribution

It introduces a vorticity-gradient force mechanism explaining the oscillations of Jupiter's polar cyclones, supported by data analysis and a dynamic model.

Findings

Cyclones oscillate with ~12 month periods and ~400 km amplitudes.

Vorticity-gradient forces correlate highly with cyclone accelerations.

A model reproduces observed oscillatory motion driven by these forces.

Abstract

The polar cyclone at Jupiter's south pole and the five cyclones surrounding it oscillate in position and interact. These cyclones, observed since 2016 by NASA's Juno mission, present a unique opportunity to study vortex dynamics and interactions on long time scales. The cyclones' position data, acquired by Juno's JIRAM instrument, is analyzed, showing dominant oscillations with ~12 month periods and amplitudes of ~400 km. Here, the mechanism driving these oscillations is revealed by considering vorticity-gradient forces generated by mutual interactions between the cyclones and the latitudinal variation in planetary vorticity. Data-driven estimation of these forces exhibits a high correlation with the measured acceleration of the cyclones. To further test this mechanism, a model is constructed, simulating how cyclones subject to these forces exhibit similar oscillatory motion.